This invention relates generally to electric motors, and more particularly to brushless DC motors with permanent magnets.
Known brushless DC electric motors typically include a motor housing, a stator, and a rotor assembly. The stator includes a stator core having a bore therethrough. The rotor assembly is rotatably mounted in the housing, extends through the stator bore, includes a rotor core and a rotor shaft extending through the core. Typically, the rotor core has at least one permanent magnet mounted thereon. The housing includes a shell and two endshields and houses at least a portion of the rotor assembly. Electric motors also include at least one bearing sized to receive the rotor shaft. The endshields attach to ends of the housing shell and support the bearings. This particular construction is conventionally known as an xe2x80x9cinner rotorxe2x80x9d motor construction. The invention described herein pertains to motors with xe2x80x9cinner rotorxe2x80x9d motor construction, as well as motors with an inside out xe2x80x9couter rotorxe2x80x9d motor construction.
During operation, the brushless DC motor utilizes electronic switching to provide torque. Typically, a motor controller receives a position feedback signal from a sensor inside the motor. The sensor ensures that excitation to the stator field always leads the permanent-magnet field to produce torque. The torque and power output of a DC motor are directly related to magnet energy level. More particularly, the amount of output is directly related to the residual induction level (Br) of the permanent magnets.
Sometimes, motor manufacturers fabricate a base motor and then develop a product line of motors with different outputs based upon the base motor but with different dimensions. For example, xe2x80x9cstacking outxe2x80x9d is a common method to vary the output. xe2x80x9cStacking outxe2x80x9d means to increase the length of the motor depending upon output needs. However, changing the length of a motor requires different length parts and raises costs for the manufacturer.
Accordingly, a manufacturer must design, manufacture, and stock parts of varying dimensions to fabricate motors with different outputs forming a typical motor product line. Typical parts with varying dimensions include a stator, a stator core, a rotor shaft, a rotor core, and a motor housing. For example, 6-inch, 8-inch, and 10-inch rotor shafts might all be utilized in the same base motor to provide different output motors obtained from increasing lengths of stators and rotors. However, designing, manufacturing, and stocking 3 different length parts is more expensive than designing, manufacturing, and stocking 1 standardized part.
A method for fabricating motors of different outputs using standardized parts includes fabricating standardized parts, ascertaining desired motor output, selecting at least one magnet from a group of interchangeable magnets to provide the desired output, and assembling a motor with the selected magnet and standardized parts such that the desired output is provided.
The interchangeable magnets have different Br values and, when interchanged in a motor, will vary the output of the motor. Since the selection is made after the standardized parts are fabricated, the output of the motor can be determined in the final stages of assembly and thus a motor manufacturer is able to respond quickly to market forces.
Accordingly, a method is provided to fabricate motors of different outputs using standardized parts wherein the output is changeable during final assembly. The invention described herein applies to motors with xe2x80x9cinner rotorxe2x80x9d motor construction, as well as motors with an inside out xe2x80x9couter rotorxe2x80x9d motor construction.